Beverage preparation machines are well known in the food industry and consumer goods domain. Such machines allow a consumer to prepare on command a single serving of a beverage such as brewed coffee, espresso coffee, tea, hot chocolate drink, or the like.
Most beverage preparation machines for in-home use operate according to a system in which beverage ingredients are provided as individually-packaged, single-serving portions. Such portions can be soft pods, pads, or sachets, but increasingly more systems use semi-rigid or rigid portions such as rigid pods or capsules. In the following, it should be understood that the beverage machine in question is a beverage preparation machine working with a rigid or semi-rigid capsule.
In many instances, the capsules for use in beverage preparation machines are sealed. Such sealed capsules are advantageous in that they protect the ingredient contained therein from the surrounding atmosphere, improving the shelf life of the capsule. Typically, such closed capsules are made from a gas and/or moisture impermeable material, and feature a rigid or semi-rigid body having one of its walls made from a flexible membrane.
The beverage is prepared by inserting the capsule into a beverage machine, which preferably comprises a receptacle for accommodating said capsule and a fluid injection system for injecting a fluid (preferably water) under pressure into said capsule. In most applications, the water injected into the capsule under pressure is heated, generally to a temperature above 70° C. However, in some particular instances it may be advantageous to inject tepid or chilled water instead. The pressure inside the capsule chamber during extraction and/or dissolution of the capsule contents is typically about 1 to about 8 bar for dissolution products and about 2 to about 12 bar for extraction of roast and ground coffee.
The present invention could also encompass the so-called “brewing” process of beverage preparation particularly for tea and coffee. Brewing involves the infusion over time of the ingredient in a fluid, most commonly hot water, whereas extraction or dissolution preparations produce a beverage within a few seconds.
For purposes of clarity, however, in this document the term “brewing” of an ingredient by a fluid is understood to encompass extraction of a powdered edible material (e.g. roast and ground powdered coffee), dissolution of edible soluble material (e.g. soluble tea, coffee, milk, or cocoa), or the infusion of an edible material in an infusion fluid under very low or atmospheric pressure, for a longer time than that required for extraction or dissolution (e.g. tea leaves in hot water).
The principle of extracting and/or dissolving the contents of a closed capsule under pressure is known and consists typically of confining the capsule in a receptacle of a machine, injecting a quantity of pressurized water into the capsule to extract or dissolve the substance, and then dispensing the resulting beverage from the capsule.
The injection is generally performed by piercing a face of the capsule with a piercing injection element, such as a fluid injection needle incorporated into the machine. Capsules applying this principle have already been described, for example in applicant's European patent no EP 1 472 156 B1, and in EP 1 784 344 B1.
In addition, machines applying this principle have already been described for example in patents CH 605 293 and EP 242 556. According to these documents, the machine comprises a receptacle for the capsule, and a perforation and injection element made in the form of a hollow needle comprising in its distal region one or more liquid injection orifices. The needle has a dual function in that it simultaneously opens the top portion of the capsule while providing an inlet channel into the capsule for the injection of the water.
The machine comprises a supply of the fluid (usually water) that is used to prepare the beverage from the ingredient(s) contained in the capsule. The machine further comprises a heating unit such as a boiler or a heat exchanger, which heats the water used therein to working temperatures (usually between 80° and 90° C.). Finally, the machine comprises a pump for circulating the water from the tank to the capsule, optionally though the heating unit. The circulation of the water within the machine may be directed via a selecting valve means, such as for instance a peristaltic valve of the type described in applicant's European patent application EP 2162653 A1.
Such systems are particularly well-adapted to the preparation of coffee. One configuration for achieving this which is particularly advantageous is to provide a capsule containing roast and ground coffee powder, which is extracted with hot water injected therein.
Capsules have been developed for such an application, which are described and claimed in applicant's European patent EP 1 784 344 B1, or in European patent application EP 2 062 831.
In short, such capsules typically comprise:                a hollow body and an injection wall which are impermeable to liquids and to air, the wall being attached to the body and adapted to be punctured by e.g. an injection needle of the machine;        a chamber containing a bed of roast and ground coffee to be extracted;        an aluminium membrane disposed at the bottom end of the chamber for retaining the internal pressure therein, the membrane being associated with piercing means which create drainage holes in the aluminium membrane when the internal pressure inside the chamber reaches a certain pre-determined value; and        optionally, a deflection means configured to break up the jet of fluid, thereby reducing the speed of the jet of fluid injected into the capsule and evenly distributing the fluid across the bed of substance at a reduced speed.        
During extraction, the beverage capsule is pierced by the fluid injection needle of the beverage preparation machine, usually in the aluminium membrane. The liquid is injected in the capsule compartment and the pressure within the capsule increases, facilitating the extraction of the beverage from the ingredients contained within the capsule.
In some implementations, the beverage machine also pierces the capsule at a second location, for instance at its bottom, permitting the beverage to flow out during the operation of the machine. In others, the beverage capsule may be provided with a spout or drain, to which is generally affixed a valve or a membrane that opens when the pressure within the capsule builds up to the level required for proper beverage preparation.
In the prior art capsules, when the fluid injection needle of the machine is removed from the capsule, after the beverage has been prepared and dispensed, the capsule top membrane is pierced and a hole “H” remains as illustrated in FIG. 1. However, in such a case, a residual pressure “P” remains within the capsule compartment due to gas that may remain trapped within the capsule under pressure.
When the capsule contains soluble ingredient to extract, the capsule compartment generally comprises a single cavity, and the residual fluid pressure is distributed across the compartment volume.
In all cases, the residual pressure P may cause a jet of liquid “J”—often referred to as “backflow”—to spray out of the hole H. Such a backflow is represented in FIG. 1. Although such a phenomenon occurs infrequently, it is undesirable to permit hot liquid to spout from the capsule. Moreover, such leakage may contain beverage ingredients, which will negatively affect the cleanliness of the beverage machine and its operation.
It is therefore an object of the invention to furnish a means for preventing backflow in a beverage capsule, in particular which is simple in construction and inexpensive to implement.